The environment is rich with ever-changing combinations of sensory stimuli which must be continuously integrated for the brain to produce a comprehensive perception of the world. Although the striking influences of multisensory integration on perception are well documented, the underlying neural bases of these effects are poorly understood. During the funding period of this grant we have found that there are specific principles guiding multisensory integration at the level of the single neuron (the superior colliculus neuron has served as our model), and that these principles are also predictive of overt behavior. It is now necessary to determine how these multisensory properties arise in the superior colliculus, and whether they represent a general set of principles that are applicable to multisensory neurons in regions of the brain (i.e., 'association' cortex) whose inputs, cytoarchitectures and functional roles are quite different. Because of the profound effects induced on a multisensory neuron when two different, sensory stimuli are present, an intriguing question has arisen which we also plan to address: is it possible that the unimodal receptive field properties of these neurons (properties which are responsible for selecting which stimuli gain access to their networks) can be significantly altered in the presence of a stimulus from another modality? If so, this would suggest that receptive field properties can be situation-dependent. Finally, using single neuron recording techniques in behaving animals we will examine how the principles of multisensory integration influence the sequence of events beginning with the processing of sensory inputs, followed by the initiation of premotor discharges, and culminating in the production of an overt response. The information from these experiments is an essential step in the development of a comprehensive understanding of the processes underlying multisensory integration.